This invention relates to a method and apparatus for separating components that are mixed in a single flowing stream of particulate material. In particular, this invention relates to a method and apparatus for detecting and removing foreign material from a stream of leaf tobacco, strip tobacco, or cut tobacco lamina filler.
Tobacco as delivered to a processing line for processing into filler or cigarettes may contain foreign matter such as pieces of the hogsheads in which it is shipped and stored, bits of string and paper, and other items. Various methods and apparatus have been used to remove these materials, including, e.g., manual observation and sorting, screens and metal detectors. However, these methods and apparatus cannot detect all forms of non-tobacco materials and many cannot operate at the high speeds characteristic of tobacco processing equipment.
It is known that certain non-tobacco materials and tobacco which is not of a desired color can be detected by optical scanning. For example, when defective cigarettes are rejected from a cigarette making machine, they are routed to ripping machines, or "rippers," which break them up and separate the tobacco filler from the cigarette paper for re-use. Some of the cigarette paper may not be removed and may be present in the tobacco filler separated by the ripper. A system exists which optically scans a layer of tobacco filler from a ripper as it travels on a conveyor belt to detect the paper. The tobacco filler is illuminated and the white paper reflects more light than the tobacco filler. The tobacco filler conveyor ends a short distance beyond the scanner, and the scanned filler is allowed to fall past an array of air nozzles. The nozzles are automatically activated to deflect those portions of the falling tobacco stream in which paper was detected by the scanner, the time needed for a particular portion of the tobacco stream to reach the air nozzles after passing the scanner being known. The deflected tobacco can then be hand-sorted to remove the paper, and put back onto the production line.
In a similar known system, leaf tobacco is inspected on a conveyor by three sensing elements made sensitive to different colors by optical filters. An integrated color mapping of the scanned tobacco is compared to the desired color, and off-color tobacco is rejected using a system such as that described above in which the tobacco falls past air nozzles which are activated automatically.
In both of these systems, tobacco is optically inspected as it passes a sensing device on a conveyor. Therefore, the sensing device will only detect those foreign materials or off-color particles which are present on the surface of the bed of tobacco on the conveyor. As a result, some foreign material will not be detected. Alternatively, a very thin "monolayer" of tobacco can be scanned, but the speed of the conveyor is limited by the speed of the scanner, so that using a monolayer greatly reduces the volume rate at which tobacco can flow through the system. This reduced rate is generally lower than that at which the remainder of the processing equipment on the line can operate and so prevents the equipment from operating at the desired speed.